Solid electrolyte compositions useful in the manufacture of solid state electrochemical devices are known in the art. In particular, solid electrolyte compositions comprising a polymeric network interpenetrated by an ionically conducting liquid phase are known.
Schawb et al., in U.S. Pat. No. 4,792,504, disclose solid polymeric electrolytes comprising a continuous network of crosslinked polyethylene oxide containing an ionic conducting phase which includes a metal salt and a bipolar aprotic solvent. The system comprises a two-phase system of a crosslinked polymer network phase which provides the structure for containing an ionic conducting phase in which a liquid complexed with a lithium salt is absorbed or interpenetrated and held as the ionic conducting phase.
Lee et al., in U.S. Pat. No. 4,830,939, disclose a similar solid electrolyte composition wherein the polymeric network is formed of radiation polymerizable compounds and the ionic conducting phase is formed of a radiation inert material.
Lee et al., in U.S. Pat. No. 4,990,413, disclose another solid electrolyte composition comprising a solid ionically conductive powder as part of the ionically conductive material contained in the polymeric network.
Shackle et al., in U.S. Pat. No. 5,037,712, disclose a solid electrolyte containing radiation curable polysiloxane materials as part of the crosslinked polymer network structure containing the ionically conducting liquid phase.
Other disclosures of solid electrolytes in this field include Bauer et al., U.S. Pat. No. 4,654,279; LeMehaute, et al., U.S. Pat. No. 4,556,614 and Andre et al., U.S. Pat. No. 4,357,610. In these patents, as well as the patents mentioned above, the polymer network which provides the basic solid structure for the electrolyte is formed from any number of polyethylinically unsaturated monomers which are polymerized or copolymerized with other monomers by various polymerization mechanisms, including radiation crosslinking. The polymeric network structure can be formed from crosslinkable polysiloxanes, crosslinkable polyethylene oxide, various acrylates, epoxy resins, polyacrylonitrile matrix resins as well as other resins appropriate for the properties desired in the solid electrolyte structure.
The ionically conductive phase, typically referred to as the liquid interpenetrating phase, typically comprises propylene carbonate, gamma-butyrolactone, 1,3-dioxolane, tetrahydrofurans, polyethylene glycol dimethyl ethers, glymes, and other materials which are capable of complexing with or solubilizing the desired lithium salt or sodium salt. Particular lithium salts, sodium salts and ammonium salts are known in the art, as disclosed in the above referenced patents.
The disclosures of the above patents are incorporated herein by reference.
It has been found that in some end use applications of electrochemical devices, such as batteries or capacitors containing the solid electrolytes, a problem has been noted in that under certain conditions the so-called liquid phase of the solid electrolyte can migrate and sometimes volatilize from the solid electrolyte. It is desirable that a solid electrolyte be provided in which the liquid phase material is held more permanently in the polymeric network structure to thereby prevent the liquid phase material from migrating or volatilizing.